The present invention relates generally to the field of traveling wave devices and tubes, and more specifically to the production of such devices containing an unific composite metallic dielectric helical slow wave structure in which the dielectric is segmented on the peripheral surface of the metallic helical element for improved balance between the heat conductive and electrical requirements of the slow wave structure.
One of the most serious problems with traveling wave devices, to which the present invention relates, has been to dielectrically support the delicate internal metallic element of the slow wave structure by means having adequate heat conductive capacity without excessive dielectric loading and subsequent reduction in the RF output of the device. The above requirements are counterproductive and can be resolved only by a judicious compromise in the design geometry of the dielectric support. For increase in RF output power, the limiting factor prior to slow wave structures in accordance with the referenced U.S. Pat. No. 4,115,721 has been the heat conductive capability of the slow wave structure.
The physics of the dual function of the dielectric helix support and the consequential problems are well known to the art, for which reason they will not be discussed in detail. It will be noted that covering the entire peripheral surface of the metallic helical structure with a dielectric will promote strong dielectric loading effects, thus changing the phase velocity, its dispersion, and the impedance of the RF circuit. In many applications these changes lead to less desirable characteristics of the circuit.
What is tolerable, or may even be desirable under some design configurations and operating specifications, will not be likewise regarded under other specific requirements. The problem is one of compromise or balance between electromagnetic and thermal circuit capability. Slow wave structures in accordance with U.S. Pat. No. 4,115,721 are ideally suited for some applications; however, in other applications it would be desirable for overall effectiveness to bias the balance somewhat in favor of the electrical requirements; or in other words, to somewhat reduce any surplus heat conductive capacity of the continuous dielectric in favor of the electrical requirements, while at the same time retaining adequate heat conductive capacity.
Slow wave structures in accordance with U.S. Pat. No. 4,115,721 are stated to be "unific" in that the metallic and the dielectric portions of the structure have been united into a whole to a far greater extent than by prior methods. The particulate deposition of the dielectric is very dense, has a superior bond, and greatly improved heat conductive capacity. As will be explained below, the present invention is to remove any surplus heat conductive capacity by segmenting the dielectric while retaining its desirable unific characteristic in relationship to the central metallic element.